Method of bonding aluminum to steel and article produced thereby



United State tm METHOD OF BONDING ALUMINUM T STEEL AND ARTICLE PRODUCED THEREBY Ralph A. Schaefer, Cleveland, and Joseph F. Cerness and Wilbert H. Morrison, East Cleveland, 'Ohio, assi'gnors to Clevite Corporation, a corporation of Ohio No Drawing. Application February 21,1951, Serial No. 212,205

9 Claims. (31. 29-1965 The present invention relates to an improved bimetallic article and a method of'producing the same. It is especially directed to an article consisting of a layer of steel and a layer of aluminum or aluminum alloy firmly bonded together in such a manner that the article is capable of withstanding severe bending, forming, or rolling without rupture of the bond.

it is a recognized fact that molten aluminum is very reactive with most metals and forms intermediate brittle phases upon solidification. This is especially true when heavy coatings of molten aluminum are in contact with relatively heavy layers of steel since the temperature cannot be lowered in sufficient time by known conventional methods to prevent the formation of detrimental brittle phases. Many attempts have been made in the past to provide means for coating ferrous base metals with aluminum by using various other metals such as copper, tin, zinc, and the like as bonding agents, but in most of these prior methods the metal used did not prevent re action between the aluminum and ferrous base metal. Other methods have been proposed, whereby the ferrous base metal was coated with a metal which in turn was contacted with molten aluminum and which acted as a barrier layer to prevent reaction between the ferrous base metal and the aluminum. Such a process is described in application Serial No. 769,616, filed August 20, 1947, now Patent No. 2,611,163, dated September 23, 1952. In this application there is described a bimetallic article having a ferrous base metal, a barrier layer of nickel or cobalt and a relatively thick layer of aluminum or aluminum alloy bonded securely together.

This application is a continuation-in-part of said above application, now Patent No. 2,611,163, and of its divisional application Serial No. 188,986, filed September 6, 1950.

As the thickness of the steel or the molten aluminum or its alloys increases, the time of heat removal is correspondingly increased. Since. the reaction rate between the molten metal and the barrier layer is proportional to the temperature and time of contact, the heavy gauge steels and heavy sections of molten aluminum 1 or its alloys will allow the formation of brittle intermediate phases of nickel or cobaltwith aluminum which in turn minimize theductility of the bond and reduce the ability of the bimetal article to withstand mechanical work. The present invention contemplates using layers of cobalt or alloys of cobalt with iron or nickel and subsequent layers of silver or alloys of silver and copper or'gold'on a ferrous base metal in combination with a layer of aluminum to give a strong, ductile bond capable of severe mechanical distortion and rolling.

It has been found that by applying a layer of silver or its alloys over cobalt or its alloys on a heavy steel section and then casting a thick layer of aluminum or aluminum alloy upon it and quenching in the conventional manner, the bond strength can be controlled to obtain a resulting product capable of severe mechanical distortion or roll- 2,759,250 Patented Aug. 21, 1956 num alloy. The exact role of silver and its alloys on cobalt or its alloys toenhance the bond strength and duetility between the aluminum and steel, is unknown.

It has been found that cobalt alloyed with iron or nickel is satisfactory in place of pure cobalt and that silver alloyed with copper or gold may be used in place of pure silver. The only explanation of why this is possibleis associated with the relationship of the metals in the periodic table. Thus cobalt alloyed with other metals in the iron group 8A and silver alloyed with other metals in the group 1B and used in combination with aluminum and steel as previously described will give a strong, ductile product.

In carrying out the-present invention, strip, sheet or plate steel is first electroplated with a layer of cobalt approximately .0001 to .0005 inch thick, although the upper limit is largely determined by economies, which layer is then covered with 'an electroplated layer of silver of .00005 to .0002 inch thickber'ore the cobalt oxidizes. Then the plated strip is heated to approximately 1350 F. in anonoxidizingatmosphere and a molten alluminum alloy at approximately 1350 F. is cast upon the plated surface. The material is quenched at a rate of approximately F. per second until a temperature of approximately 1000 F. is reached, to solidify the aluminum. Below this temperature the rate of quench is immaterial. Alloys of cobalt'with iron or nickel may be substituted for the cobalt and alloys of silver with copper or gold for the silver.

Inorder'to evaluate the ductility of the bond between the steel and aluminum layers, a chisel test, a bend test, and a rolling test have been used. The chisel test consists of using a cold chisel and a hammer and attempting to separate the aluminum from the steel by pounding the chisel at about a 30 angle to the surface of the material between the layers. The bend test consists in bending a blank at 180 upon itself with the aluminum layer on the outside. The rolling test consists of reducing the composite by rolling in conventional rolling equipment to a minimum reduction of 25%. Material made in accordance with the invention will withstand the ductility tests described above and in addition can be annealed at temperatures up to- 1000 F. in a neutral atmosphere for a conventional period of time without affecting the bond strength or ductility, which is not possible with other bonding media for aluminum and steel. If the material passes these three tests it is considered satisfactory for complex forming and fabricating processes. Previously known'bondingcombinations, especially when there is a relatively thick layer of aluminum and of steel, will not withstand these tests without rupture of the bond.

The following is a specific example of one method of carrying out the invention. Low carbon cold rolled steel strip such as S. A E. 1010 approximately 4.5 inches wide by 0.131 inch'thick was properly cleaned and pretreated according to regular commercial plating practice and was then electroplated with a layer of cobalt approximately .0002 inch thick, followed by an electroplated layer of silver approximately .0002 inch thick be fore anoxide film was formed on the cobalt so as not to interfere with the adhesion of the silver to the cobalt. These plating operations were carried out in standard electroplating baths by conventional methods. The plated steel strip was then heated in an atmosphere furnace containing approximately 90% nitrogen and 10% hydrogen to a temperature of 1350 F. and had east upon the plated surface a molten aluminum alloy consisting of approximately 1.5% silicon, 6.5% tin, 1% copper, 0.5% nickel, balance aluminum with normal impurities at 1350 F. The strip was then quenched with water from the ferrous side as described in application Serial No. 769,616, now Patent No. 2,611,163, dated September 23, 1952. This material will withstand tests indicated above for bond strength.

An example of the other barrier layers includes alloys of cobalt and iron or nickel in a ratio of approximately 50% each. The silver layer may include copper or gold of the 1B group of the Periodic Table in a proportion of 50% silver and 50% copper or gold. In most instances the percentage of silver should be greater than In most cases the layers of the cobalt alloys and the silver alloys will be electrodeposited but the latter layer may be successively deposited and then diffused, with silver usually being the outer layer.

It has been found that the invention is particularly advantageous when used with steel thicknesses in excess of .080 inch and layers of aluminum in excess of .020 inch thick when the cooling rate is approximately 100 F. per second. Below these thicknesses the invention is also advantageous but generally the heat can be extracted from thinner sections fast enough to prevent formation of the undesirable intermediate phases.

Steel in the form of sheet, strip, tubing, or the like which is prepared with a layer of cobalt or its alloys and a layer of silver or its alloys as described and which is subsequently cast with aluminum or an aluminum alloy will produce a bimetallic article having greatly improved bond strength over present known combinations.

It is to be understood that this invention is not confined to the precise details herein set forth in the preferred manner of carrying out this invention as it is apparent that many changes and variations may be made by those skilled in the art without departing from the spirit of the invention or exceeding the scope of the appended claims.

We claim:

1. A method of making a bimetallic material composed principally of a ferrous layer and a layer of aluminum or aluminum alloy which consists of electrodepositing a layer of metal selected from the iron group or its alloys in which cobalt is at least 50% of the alloy and successively coating upon this layer a second layer of a silver group metal before said cobalt layer oxidizes and lastly casting upon said silver group layer a layer of aluminum.

2. The method of making a bimetallic material composed principally of a layer of ferrous material and a layer of aluminum or aluminum alloy integrally bonded thereto which consists of plating a metal barrier layer selected from the group consisting of iron, cobalt, nickel or their alloys in which cobalt is one of the metals and at least 50% of the alloy and subsequently coating said barrier layer with a metal from the group consisting of silver, copper, gold or their alloys and before said cobalt layer oxidizes in which the silver content is over 20% and casting upon said latter layer molten aluminum.

3. A method of making a bimetallic material composed principally of steel upwards of .080 inch thick and aluminum or aluminum alloy upwards of .020 inch thick which consists of plating upon said steel a metal barrier layer selected from the group consisting of cobalt, nickel, iron or their alloys provided cobalt is one of the metals and at least 50% of the alloy and coating said barrier layer with a second layer from the group consisting of silver and its alloys with copper or gold before said cobalt layer oxidizes and casting upon said second layer a layer of aluminum in a reducing atmosphere composed principally of nitrogen and a small percentage of hydrogen and subsequently quenching the aluminum to minimize the reaction between the molten aluminum and the barrier layer.

4. A method of making a bimetallic material composed principally of a layer of ferrous material more than .080 inch thick and a layer of aluminum or aluminum alloy more than .020 inch thick which consists of plating upon said ferrous material a metal barrier layer selected from the group consisting of cobalt, nickel, iron and alloys thereof wherein cobalt is one of the materials from .0001 to .0005 inch thick and at least 50% of the alloy and coating said barrier layer with a metal selected from the group consisting of silver, copper and gold from .00005 to .0002 inch thick and before said cobalt layer oxidizes and casting upon said strip at a temperature of about 1350 F. in a reducing atmosphere a layer of aluminum or aluminum alloy and quenching said molten aluminum from the ferrous side of the strip to solidify the aluminum at a quenching rate of at least F. per second.

5. A bimetallic article comprising a steel layer and a layer of aluminum or aluminum alloy upon said steel layer, having interposed therebetween a layer of cobalt alloy in which the cobalt is at least 50% of the alloy bonding the layers throughout their contiguous surfaces into separate and distinct layers.

6. A bimetallic article composed principally of a layer of steel and a layer of aluminum or aluminum alloy upon said steel layer, completely bonded together by means of a bonding layer of cobalt all over their contiguous surfaces, which cobalt layer has a reaction zone with the aluminum having a minimum formation of brittle intermetallic phases.

7. A bimetallic article comprising a layer of ferrous material greater than .080 inches and a layer of aluminum or aluminum alloy in excess of .020 inch, having interposed therebetween, throughout their contiguous surfaces, a layer of cobalt, with which there is a minimum formation of brittle intermetallic phases of cobalt at the bond line with the aluminum or aluminum alloy.

8. A bimetallic article comprising a steel layer and a layer of aluminum or aluminum alloy upon said steel layer, having interposed therebetween a bonding layer of a member of the group consisting of cobalt, iron and nickel and alloys thereof, in which cobalt is at least 50% of the alloy, and further, in which said bonding layer secures the aluminum and steel together completely throughout their contiguous surfaces.

9. The bimetallic article of claim 6, in which the bonding layer has a thickness of 0001-0005 inch.

References Cited in the file of this patent UNITED STATES PATENTS 1,792,082 Fink Feb. 10, 1931 1,863,809 Hopkins Jan. 21, 1932 2,082,622 Fink June 1, 1937 2,119,304 Viers May 31, 1938 2,145,248 Ch-ace Jan. 31, 1939 2,269,523 Deutsch Ian. 13, 1942 2,459,161 Harris Ian. 18, 1949 2,473,712 Kinney June 21, 1949 2,490,543 Robertson Dec. 6, 1949 2,490,549 Schultz Dec. 6, 1949 2,531,910 Hensel Nov. 28, 1950 2,539,247 Hensel Jan. 23, 1951 

6. A BIMETALLIC ARTICLE COMPOSED PRINCIPALLY OF A LAYER OF STEEL AND A LAYER OF ALUMINUM OR ALUMINUM ALLOY UPON SAID STEEL LAYER, COMPLETELY BONDED TOGETHER BY MEANS OF A BONDING LAYER OF COBALT ALL OVER THEIR CONTIGUEOUS SURFACES, WHICH COBALT LAYER HAS A REACTION ZONE WITH THE ALUMINUM HAVING A MINIMUM FORMATION OF BRITTLE INTERMETALLIC PHASES. 